One problem that is common to many data communications technologies is the corruption of data due to noise. The signal-to-noise ratio (SNR) for a communications channel is an indication of the quality of the communications carried out over that channel, as it conveys the relative strength of the signal that carries the data (as attenuated over distance and time) to the noise present on that channel. These factors relate directly to the likelihood that a data bit or symbol received over the channel is in error relative to the data bit or symbol as transmitted. This likelihood is reflected by the error probability for the communications over the channel, commonly expressed as the Bit Error Rate (BER) which is a ratio of bits that are received and decoded in error to total bits transmitted. In general, the likelihood of error in data communications should be considered in developing a communications technology. Techniques for detecting and correcting errors in the communicated data should be incorporated for the communications technology to be useful.
To this end, error detection and correction techniques are implemented through the use of redundant coding of the data. In general, redundant coding comprises inserting data bits into the transmitted data stream that do not add any additional information, but that indicate whether an error is present in the received data stream. More complex codes provide the ability to deduce the true transmitted data from a received data stream, despite the presence of errors.
One decoding technique is known as layered decoding. Layered decoding, described in detail below, generally comprises processing the rows of a parity check matrix in groups, or layers. Each layer is processed in successive order, and the processing of each layer is dependent upon data obtained from the processing of an immediately preceding layer. However, these decoder architectures are designed such that there is an inherent data latency between the processing of each layer. For example, to begin processing a layer in a parity check matrix, data obtained by processing the preceding layer must first be obtained. However, this data may not be immediately available; instead, the data may still be in the decoder pipelines, en route to a destination point from which it may be collected to be used for processing. Such data latency causes decoder performance to suffer.